What is the working principle of a ramp type Digital Voltmeter (DVM)?
The working principle of a ramp type Digital Voltmeter (DVM) is based on the comparison between an unknown input voltage and a linearly increasing or decreasing reference voltage, known as a ramp signal. In simple terms, the meter measures how long it takes for the ramp voltage to reach the same level as the input voltage. This time interval is directly converted into a digital value, which represents the measured voltage on the display. The main components involved are a ramp generator, comparator, clock pulse generator, and counter circuit.
Here’s how it works step by step. When a measurement starts, the ramp voltage begins to rise or fall at a constant rate. The comparator continuously compares the ramp voltage with the input voltage. As soon as both voltages become equal, the comparator sends a signal to stop the counter. The counter, driven by clock pulses, has been counting the time taken during this interval. Since the ramp rate and clock frequency are fixed, the total number of counts is proportional to the input voltage. This count is then processed and displayed as the digital voltage reading.
In short, a ramp type Digital Voltmeter converts the analog input voltage into a time-based digital count. The longer the ramp takes to match the input voltage, the higher the displayed value. This method provides good accuracy and stability for medium-speed measurements. However, it is slower compared to other DVM types like dual-slope or successive-approximation voltmeters. Still, the ramp type DVM is widely used in educational instruments and lab setups due to its simple working principle and easy implementation.